Muffle



Aug. 26, 1958 E. C. SENGER MUFF'LE Filed Dec. 4, 1956 INVENTOR Sdwon a 5ATTORNEY United States Patent MUFFLE Edwin C. Sanger, Fairfield, Conn.,assignor to Rolock,

Incorporated, Fairfield, Conn., a corporation of Connecticut ApplicationDecember 4, 1956, Serial No. 626,129

9 Claims. (Cl. 263-47) This invention relates to apparatus useful in theheat treating of metal parts whether tray conveyed or ad vanced inrunning lengths through a heat treating zone and especially concernsapparatus for processing such work at high temperatures in the presenceof a special gaseous medium. Where an open furnace is the source of heatit is common to advance the work through a gas isolating passageway orelongate oven that spans the combustion chamber of the furnace and isopen at both ends outside of the furnace walls which serve to supportthe oven near opposite ends thereof. Such passageway form of oven iscommonly termed a muffle. The gaseous mediums employed therein may havea high content of hydrogen or nitrogen and must be dependably guardedagainst escape or leakage into the combustion chamber of the furnace.

Muflies for the above purpose are long hollow structures of tubularnature in various cross sectional shapes and usually comprise a hoodsection arched over and joined to an underlying hearth section so as tohouse a long passageway desired to have gas-tight, heat pervious walls.Because of the high temperatures involved and a requirement that themetal walls be as thin as possible in order to promote even and rapidtransfer of heat from the furnace to the muffle interior, muffies asheretofore constructed have lacked sufficient tubular rigidity whenweakened by heat to resist inward collapse of the roof wallof the hoodsection and/or sagging of the muffle as a whole in its span that bridgesthe combustion chamber of the furnace. Further troubles have resultedfrom the tendency of the mufile' walls to distort and rupture whensubjected to stresses and strains of thermal shock caused by feedingcold work into the receiving end of a mufile while the latter is veryhot. The cold work contacts and abruptly cools only the hearth sectionof the muflle on which it rests such cooling being unaccompanied bysimultaneous cooling of the hood section of the mufie. There takes placea sudden contraction of the cooled hearth section both in lengthwise andcrosswise directions which is strongly opposed by the still hot walls ofthe hood section. Means have therefore been needed to compensate for awide and suddenly occurring difierential of discordant expansion andcontraction between the different sections of the muflle. I

While it has been proposed to add external ribbing to the mufile wallsto reinforce them against collapse or sagging it adds objectionableweight, and such form of reinforcement has been found to weaken undulythrough overheating because of its relatively greater mass exposed tothe intense heat of the furnace and to increase the occurrence. ofcracks and the breaking of seams in the muffle walls. Internal ribbingof the mufile walls can not be resorted to without sacrificing badlyneeded cross sectional space in the passageway formed by the muflle andthis reduces the rate of work output from a rnufile of given tubulargirth.

An object of this invention is to utilize new mechanical principles inthe construction of muflies enabling the walls I 2,849,222 Patented Aug.26, 1958 thereof to be made of sufliciently thin sheet metal tofacilitate heat transfer therethrough without sacrificing needed tubularstiffness of the muffle, whereby a very long, light weight mufflecapable of eficient heat performance is enabled to bridge the hightemperature chamber of a heat treating furnace without sagging under itsown weight alone or when augmented by the weight of its contained workload.

Another object is to avoid introducing into the structure of a mufileany strengthening reinforcement that will add materially to the muffleweight or harmfully oppose widely unequal extents of expansion andcontraction that take place in different sections of the mufllerespectively in response to temperature differentials induced asaforesaid.

The foregoing and other objects of the invention will become clear infuller detail from the following description having reference to theaccompanying drawings wherein:

Fig. 1 is a perspective view of a muffle embodying the presentimprovements removed from the combustion chamber of a heat treatingfurnace.

Fig. 2 is a view looking at either end of the muffle of Fig. 1.

Fig. 3 is an elevation showing the rnufille partly in longitudinalsection on the plane 33 in Fig. 2.

Fig. 4 is a view taken in cross section on the plane 44 in Fig. 3looking in the direction of the arrows.

Fig. 5 is a view similar to Fig. 4 showing a modified cross sectionalshape of mufile.

Fig. 6 shows a modified corner construction of the muffle of Fig. 4.

In Figs. 1 to 4, inclusive, the mufflle comprises an elongate, openended, oven forming enclosure the main part of whose length comprisesmerely the assembly of a hearth section 12 and a hood section 13. Thepresent improvements reside partly in features of construction of thewalls of these individual sections and partly in the cooperativereaction between the sections when united and spanning the heat chamberof a furnace.

It has been proposed heretofore to fabricate muffies of suificientlythin sectional sheet metal walls to permit an acceptable rate of heatflow from the combustion chamber of the oven through the walls of themufile to the interior thereof. But such mufiles have lacked thetubularstrength and rigidity required to prevent sagging or rupture inthe high temperatures required for many heat treating processes.

The present improvements overcome this and other problems by providingthe hearth and hood sections with cooperative patterns of corrugationsrelated so as not only to impart rigidity but also to compensate for thehereinbefore mentioned wide differentials of expansion and contractionbetween the sections due to powerful discordant forces of expansion andcontraction in the mufile walls.

To this end each of the corrugations 14 in hood wall 13 extendsthroughout the arched shape of the wall crosswise the mufile fully toand terminating at downward directed bottom edges of the hood Wallbetween points on opposite sides of the latter where the hood wall meetsrim portions of the hearth sections 12 comprising parts 16 and 17. Thuscorrugations 14 strengthen the ability of hood wall 13 to support itsown arched formation crosswise of the muffle without collapsing whileimparting to the hood section an ability to stretch lengthwise of themuffle in accordion fashion and thus accommodate expansion andcontraction of the hearth wall 12 lengthwise-of the muffle occasioned bytemperature changes.

Corrugations 15 extending lengthwise in the floor wall 12 of the hearthsection help to stiffen it lengthwise against sagging while at the sametime because they are separate from corrugations they can flex to permitmechanical expansion and contraction of the hearth section crosswise ofthe mufile instead of imposing stresses and strains on the hood sectionof the muffle tending to flex the arched hood Wall. Such'corrugations 15in the floor wall 12 of the hearth section are disposed lengthwise ofthe mufile between the opposite lateral rim portions of the hearthsection. They also form upstanding work supporting ridges serving as thesole points of support presented to cold work metal when introduced intothe mufile for heat processing, and thus prevent the work fromextracting as much heat from the metal of the hearth wall as would bethe case if the floor wall 12 were fiat and in surface contact with thework metal over a larger area,

From the foregoing description and in all figures of the drawings itwill be seen that the ends of corrugations 14 are in edgewise contactalong an undulating course with the upward facing relatively broadsubstantially plane surfaces of rim portions 17, 23 of hearth section12, practical and differing cross sectional shapes of which rim portionsare shown in Figs. 4 and 6 respectively. In Fig. 4 the sheet metal ofthe hearth section is bent throughout the length of its marginalportions to extend first upward forming a vertical web 16 rising fromfloor wall 12 and then laterally inward of the mufl'le to form ashelf-like lip 17 against whose upward facing surface the downwarddirected edges of the corrugated hood wall 13 abut in the aforesaidundulating cause at a height above the level of the floor wall 12 equalto the vertical extent of web 16. All points of meeting or joinder ofthe hood wall to the hearth section throughout the length of the mufllemay now be welded continuously along the said undulating cause from theoutside of the muffle as at 18 to form a gas-tight seal and to unify thehood wall and the hearth section into an elongate tubular structurehaving the following advantages.

The corrugations 15 in the floor wall 12 of the hearth section reducethe amount of floor surface area with which the work resting on orsliding through the muffle comes in contact. These corrugations inconjunction with the web 16 acting as a diaphragm provide flexibility inthe hearth section capable of absorbing expansion and contractionthereof crosswise the muffle without forcefully transmitting distortiveforces to the hood wall 13. Corrugations 14 in the hood wall increaseits rigidity in directions radial to the arch of the hood wall and thusfortify it against inward or downward collapse without the need ofextraneous reinforcement. Cor-rugations 14 further permit accordion-likeexpansion and contraction of the hood wall lengthwise of the muffle sothat it does not forcefully resist longitudinal expansion andcontraction of the hearth section.

From the foregoing cooperative functions of the corrugations in the hoodwall and in the floor wall of the hood section combined with lateralflexibility of web 16 there results a muffle of minimum weight, highheat permeability and maximum strength against sagging as well assufficient relief from the distortive effects of heat to impart longlife and increased endurance without the rupture and leakage heretoforeoccurring at sectional joints and elsewhere in the sheet metal walls ofmuffles as formerly constructed.

At each end of a muffle section constructed as above, there may beappended a terminal or throat section 19. Such throat section maycomprise a sheet metal work entrance or discharging passageway 19 whosedome wall has downward directed edges welded to the shelf 17 as are theedges of the hood wall 13 and having its rear edges welded to theforward end of the hood wall. If the height of throat section 19 is lessthan that'of the hood wall 13, as is shown to be the case in Figs. 1, 2and 3, the open gap that results will be closed by a crescent shapedvertical plate 20 having its edges welded to both the hood wall and thethroat Walls to complete gastight closure therewith,

At extreme ends of hearth wall 12, which project beyond and in outboardrelation to the length of hood wall 13, there may be a vertical flangeplate 21 bordering the open end of throat section 19 and welded fixedlythereto, plate 21 sometimes containing holes 22 to receive bolts forfastening the flange plate 21 to mating pieces of equipment (not shown).

In Fig. 6 the hearth wall 12 differs from hearth section in Fig. 4 bypresenting a shelf-like lip 23 protruding from the web 16 laterally inan outward direction rather than an inward direction otherwise likeshelf 17 with respect to the muflle. The hood wall 13 is then welded inedgewise abutting contact with lip 23 in the same manner as with shelf17 in Fig. 4.

In the differing constructions of Figs. 4 and 6 there is the advantagethat the extreme lower and outermost corners 24 of the muffle areentirely free from joints and consist solely of a smooth bend of thesheet metal of the hearth wall 12 wherefore there are no snags, as fromwelded joints, to become disrupted in handling the muflle nor seams togive way at this very vulnerable point in the construction.

The appended claims are directed to and intended to cover the foregoingand all other equivalents differing from the particular shapes andarrangements of parts herein disclosed which fairly come within a boardinterpretation of the definitions of the invention a worded in theclaims.

I claim:

1. A muflle having walls highly pervious to heat adapted to bridge ahigh temperature chamber in a heat treating furnace without sagging,comprising in combination, a channel-shaped sheet metal hearth sectionincluding a floor wall and marginal rim portions each presenting arelatively broad substantially plane surface continuous lengthwise ofthe muflie, and a sheet metal hood wall arched over the width of saidhearth section and having corrugations running crosswise of the muffledisposed to form alternate ridges and grooves each following the arch ofsaid hood Wall and extending fully to and terminating at downwarddirected bottom edges thereof in a manner to impart undulating contourthereto in a line of meeting with said plane surface, said undulatingbottom edges being united respectively withsaid plane surface in amanner to form a gas-tight joint therebetween.

2. A mufile as defined in claim 1, together with a hollow throatstructure forming a continuation of the passageway through said mufflesecured rigidly to both the said hearth section and to the said hoodwall including flanges outwardly bordering said continuation of thepassageway for anchoring the muffle to mating pieces of equipment.

3. A muflle as defined in claim 1, in which the said marginal rimportions of the said hearth section each comprises a laterally extendingshelf-like lip portion having an upward facing relatively broadsubstantially plane surface extending straight and continuous lengthwiseof the muflle spaced above the said floor wall.

4. A muffle as defined in claim 3, in which the said downward directededges of the said hood wall abut against the said plane surfaces of thesaid lip portions and are secured fixedly thereto.

5. A muffle as defined in claim 3, in which the said rim portions of thesaid hearth section each comprises a bent formation of continuous sheetmetal of the said hearth section including a flexible web portion risingfrom the said floor wall and a shelf-like lip portion having an upwardfacing relatively broad substantially plane surface extending laterallyfrom said web portion inward of the mufl le.

6. A muflle as defined in claim 5, in which the said undulating edges ofthe said hood wall abut in an undulating course against said planesurfaces .of the said shelflike lip portions respectively and aresecured fixedly thereto.

7. A muffle as defined in claim 3, in which the said rim portions of thesaid hearth section each comprise a bent formation of continuous sheetmetal of the said hearth section including a flexible web portion risingfrom the said floor wall and a shelf-like lip portion having an 5 upwardfacing relatively broad substantially plane surface extending laterallyfrom said web portion outward of the muffle.

8. A muflie as defined in claim 7, in which the said undulating edges ofthe said hood wall abut in an un dulating course against said planesurfaces of the said shelf-like lip portions respectively and aresecured fixedly thereto.

9. A mufiie having walls highly pervious to heat adapted to bridge ahigh temperature chamber in a heat treating furnace without sagging,comprising in combination, a channel-shaped sheet metal hearth sectionincluding a floor wall having corrugations of continuous linear extentin the sheet metal thereof running lengthwise of the muffle betweenopposite lateral margins of said floor 10 a gas-tight jointtherebetween.

References Cited in the file of this patent UNITED STATES PATENTS951,556 Bossingham Mar. 8, 1910 1,268,583 Knox June 4, 1918 2,144,374Hofiman Jan. 17, 1939 2,381,538 Harris Aug. 7, 1945 2,783,987 GilbertMar. 5, 1957

